This work attempts to elucidate brain structures involved in the mediation of sodium appetite which is an innately organized behavior system in the rat and is utilized as a model for study of the general modes of neural organization underlying complex innate behavior patterns. Brain lesioning techniques are employed in a systematic program aimed at identifying critical structures and elucidating their functions with regard to monitoring of homeostatic conditions, processing of gustatory input, control of motivation and reinforcement, and modification of innate patterns by learning experiences. Three brain structures which play critical roles in the behavior system and which are closely related both structurally and functionally will be studied in detail. These structures are the lateral area of the hypothalamus, the medial region of the ventral posterior thalamus, and the amygdala. The effects of damage to each of these structures will be compared. The phenomena to be studed include the relation between amount of tissue damage and the intensity of behaviorial impairment, interactions of preoperative learning experiences and lesion induced deficits, effects of postoperative learning upon recovery of function, gustatory preference-aversion behavior, renal function in response to sodium deprivation, and patterns of alimentary deficits.